1. Field of the Invention
The present invention concerns a method for the removal of organic components from a mixture of organic components and water, in particular for the removal of oil from an oil in water emulsion.
In particular, the method is meant for the removal of oil from the condensate of an oil-lubricated compressor, but the method concerned by the invention is not restricted thereto.
2. Discussion of the Related Art
It is known that, when two non-mixable liquids such as oil and water are put into contact, one liquid can be distributed in the other one via dispersion without dissolving and forming a homogenous phase. The dispersion of one liquid in the other one is called an emulsion.
In processes whereby water and oil can condense together and/or can be turbulently mixed, such as in an oil-lubricated compressor, an emulsion is often found in the resulting condensate which can survive a long time, especially when the condensate contains substances which can act as emulsifiers or when the oil has a detergent character. The period of time during which the condensate of an oil-lubricated compressor makes contact with the purifying elements of the installation for condensate treatment is often shorter than the “life span” of an induced emulsion (if this life span were measured in a separate vessel). Apart from this induced emulsion, there usually is a separate oil phase as well.
Two basic groups of emulsions are known: water in oil emulsions, in short WO emulsions, and oil in water emulsions or what are called OW emulsions. The present invention can be used in the field of OW emulsions, whereby drops of oil are distributed in a water phase.
Methods are already known whereby a mixture of organic components and water is put in a vessel in which an amount of “organoclay” is present and whereby organic components are sorbed by the “organoclay” and thus removed from the mixture.
By “organoclay” is meant a reaction product of a clay with a quaternary ammonium compound. Examples of organoclays are described among others in U.S. Pat. No. 2,531,427, U.S. Pat. No. 2,966,506 and U.S. Pat. No. 3,422,185.
The application of organoclay for the removal of organic components from a mixture of organic components and water is described for example in U.S. Pat. No. 4,549,966, in which is described a method whereby a mixture of organic components and water is put into contact with organoclay for a certain period of time so as to allow an amount of the organic components to be sorbed by the organoclay. This contact is induced in a “packed tower”, a “fluidized bed” or a “stirred bed”.
In a packed tower, the organoclay particles practically stay in the same place whereby, in a continuous process, an OW emulsion flows along. A packed tower has been designed such that no other flow is possible than in one direction through the structure with solid matter, whereby the latter covers the entire section. The design must then allow for an optimal ratio between the pressure drop and the contact time.
In a fluidized bed or stirred bed arrangement, the organoclay particles are set in motion by a gas flow, by a mechanical agitator respectively, and they are maintained in suspension through an OW emulsion.
A first disadvantage of the existing method whereby organoclay in a packed tower is used, is that the OW emulsion must stay relatively long in contact with the organoclay in order to obtain good separation results. This can be explained in that the organic components are surrounded by water molecules which hinder the sorption. A packed tower must then be made relatively large or complex (e.g. with recirculation) to make it possible for a continuous flow to be purified sufficiently.
The major disadvantage of a packed tower, however, is the pressure drop. At the start it is still relatively small and the OW emulsion still flows through smoothly. After having absorbed organic components, practically all organoclays have the property to swell and to thus hamper the flow-through. Since a packed tower has been designed to guarantee the contact between the OW emulsion and the organoclay over the entire cross section, there is no space for cross expansion of the organoclay, and so the latter will easily clog gradually during the process.
Further, packed tower arrangements have been designed such that the supplied flow, in this case the emulsion, only touches one surface of the solid structure, in this case the organoclay, and can reach the entire structure via this surface.
Another disadvantage is a that it is difficult to introduce new organoclay and to remove saturated organoclay. A fluidized bed or a stirred bed is usually applied in batches, and thus it is not very appropriate for continuous processes, unless a complex automation is introduced. As mentioned in U.S. Pat. No. 4,549,966, the organoclay must be filtered, centrifuged or flocculated to be separated from the OW emulsion again.
Fluidized or stirred bed arrangements have a bad reputation in that the particles that are put in suspension wear out under the influence of the agitation. This results in a continuous creation of organoclay particles with diameters that are too small to be collected in a filter. Downstream of this type of arrangements, a cyclone separator is usually installed to separate the worn-out small particles of organoclay.
Another known method for separating oil and water from a mixture thereof consists in leading the mixture of oil and water through a chamber in which has been provided a filter of oleophilous (oil-attracting) material, such that oil can be adsorbed from the liquid mixture of oil and water. An example of such a floating filter is described in EP 1,185,347, the complete description of which has been enclosed here by way of reference.
Although, in general, such filters produce good results, it may be that, under circumstances such as those whereby an emulsion is being formed, such a floating filter, even combined with an after treatment with an active carbon filter and/or combined with a coalescent organ, sometimes is not sufficient to obtain sufficiently purified water. For, the life of the induced emulsion sometimes lasts longer than the contact time with the purifying organs, whereby these purifying organs have not been specifically designed to absorb the distributed oil drops from an OW emulsion.